Start un-initializing kernel devices and drivers. Shut down each device so that it's state is saved and it will exit gracefully. This is where most Win9x shutdown hangs occur, due to poorly written device drivers.

The concept of disk checking on Windows-based fat16 systems was originally put together by Peter Norton, the Norton Utilities guy in the form of chkdsk 4.0 for DOS. (Unix had disk checking on their filesystems long before Windows.) Scandisk saw the light of day with DOS 5.0 with the advent of Smartdisk, disk caching software responsible for many lost clusters. The Nortontrademark was eventually purchased by Symantec, who created what went on to become Windows Scandisk). Microsoft, after seeing the benefits of regular system maintenance, Scandisk was included with the software diagnostics that went into the original Windows 95, even though Norton kept publishing it's toolkit (with many added features). Microsoft licenced this technology from them, no doubt for quite a sum, seeing the distribution of all of the OS's.

It should be noted that shutting down from single-user mode, or MS-DOS mode (the VGA graphic you see is on some systems just on top of a DOS prompt) is usually fairly safe. There is very little OS to worry about, and there are not usually a lot of daemons and behind-the-scenes items to worry about. This is typically the point of these modes. Windows NT 4.0 brings you to a VGAGUI screen where it says it is safe to shut down. It is only holding the bare minimum of drivers in memory when it does this, and all the disks are unmounted from the kernel.

Another very rare, but possible problem with just slamming the power button off on your machine while it is running is that of a power flash across the board. It isn't likely, but it is possible that the machine lets go of all the juice a little funny, and some of it does some damage to the circuits on the way out. Violently jerking the power on and off to a system is not good for it, and can cause serious damage over time. Many computers that have been mistreated you will find have "flukey" hardware troubles compared to people who maintained their systems.

Doing what your computer thinks is best is almost never a bad thing when it comes to maintenance. My advice to you is to never skip that disk check unless you want to take that chance (or you know it's absolutely wrong). Disk damage on the file system level can and does happen this way everyday. It's best to stay on top of it before it spreads and causes damage elsewhere on your system.